1. Field of the Invention
The invention relates to a process for adjusting a motor vehicle part between at least two positions and a drive device for a motor vehicle part which can be adjusted between at least two positions.
2. Description of Related Art
Published German Patent Application DE 43 21 264 A1 discloses a generic process and a generic drive device. Here, an electric motor drives a motor vehicle window pane. By means of two Hall sensors which are offset by 90 degrees and which interact with a magnet located on the motor shaft, a signal is produced from which the instantaneous period duration of a motor revolution and thus the instantaneous motor rpm are determined at each time at which one such signal enters a control unit for controlling the motor. As soon as the instantaneous rpm change resulting from the difference of two successive rpm measured values exceeds a stipulated threshold value, the motor is reversed in order to release a possibly pinched article.
Published German Patent Application DE 195 11 581 A1 discloses a similar drive device in which, however, the threshold value is variably chosen depending on the position, a memory for certain positions of the adjustment path storing the speed change acquired in an earlier run between two adjacent positions, in order to compute therefrom as a function of position depending on the last currently acquired position and speed the shut-off threshold for the speed.
Published German Patent Application DE-OS 29 26 938 discloses acquiring the motor rpm in a sliding roof drive at uniform time intervals, finding the differences of successive values, adding these differences to one another when they are larger than a predetermined threshold value, and triggering the shut-off or reversal of the motor as soon as the added sum exceeds a predetermined threshold value.
Published German Patent Application DE 43 12 865 A1 discloses a drive device for a motor vehicle window which acquires the motor rpm by means of two Hall detectors, and which reverses the motor when a threshold is exceeded for the relative change of rpm. In doing so, the threshold value is continually recomputed depending on the acquired motor voltage and the ambient temperature which is determined by a temperature sensor on the motor. In doing so, the status/operating times of the motor are considered in order to be able to draw conclusions about the ambient temperature from the motor temperature.
Published German Patent Application DE 196 18 219 A1 and its corresponding U.S. Pat. No. 6,070,116, disclose determining the rpm threshold or the rpm change threshold of the motor, starting from which reversal of the motor takes place, from the position-dependent rpm data of a reference run which has taken place beforehand depending on the position of the cover for a sliding roof drive. More specifically, to prevent faulty actuation of motor reversal or stoppage, a calculated value is produced from a set of measured values and is compared with two limit values, and only when both limit values are exceeded, is the motor stopped or reversed.
Published European Patent Application EP 0 592 927 A1 and German Patent DE 42 34 501 C2 disclose a control for a building door, both the intensity being evaluated by an electric motor which drives the door and the rpm of the electric motor being evaluated in two parallel evaluation paths in order to detect a case of pinching, this taking place by means of a logic circuit for the two paths. In this way, provisions are made for redundancy for the failure of one of the two evaluation paths, in order, in this case as well, to still achieve reliable pinching protection.
International Patent Application Publication WO 92/20891 discloses pinching protection for moving motor vehicle parts, for example, windows or sliding roofs, the motor current being acquired, and in the first evaluation channel, the instantaneous motor current being compared to a peak current which has been acquired by a peak detector, and in the second evaluation channel, the current measurement signal being routed through filters connected in parallel with different time constants, the two filter outputs being compared to one another in a comparator. The two comparator outputs are used in a monitoring circuit as the input signal; in the first mode, a case of pinching being detected according to the signal of the first comparator, and in the second mode, a case of pinching being detected according to the signal of the second comparator. There are two parallel evaluation channels to detect pinching of a soft or a hard obstacle.
The defect in these generic drive devices which acquire the rpm is that they can be optimized, for example, by the choice of the trigger threshold only for one pinching speed, i.e., one stiffness of the entire system. The stiffness of the entire system is composed of the stiffnesses of the drive mechanism, of the pinched body, and of the motor vehicle body. On the one hand, the stiffness of the pinched body depends on the type of body. On the other hand, the stiffness of the vehicle body depends largely on the location at which the body is pinched. Thus, the stiffness can vary from one case of pinching to another, by which, in the known systems, only a small portion of the pinching cases can be optimally recognized.
The object of this invention is to devise a drive device for a motor vehicle part which can be moved between at least two positions and a process for adjusting a movable motor vehicle part between at least two positions, by which more reliable acquisition of pinching of an article is acquired.
This object is achieved in accordance with the present invention by a process and by a drive device as described in detail below.
In accordance with the invention, it is advantageous that acquisition by the pinching protection system can be optimized for at least two different pinching scenarios.
In one advantageous development of the invention, it is determined whether the first value determined in a first computation for the action of a force exceeds a given first trigger threshold or whether the second value determined from a second computation for the action of a force exceeds a given second trigger threshold, the results of the two comparisons being combined in an OR operation. This represents an especially simple acquisition of pinching.
Preferably, the first computation and the second computation are optimized for recognition of the fastest or slowest changes of the action of the force which can be expected. This forms reliable pinching acquisition in a range of pinching scenarios as wide as possible.
Preferably, in the second computation, a new value of the action of the force is computed only after each n-th input of a pulse signal (i.e., a set number of pulse signal inputs), while in the first computation, the instant of input of each pulse signal on the control unit is acquired, and between two such input instants, at certain extrapolation instants from at least some of these measured instants, the first value for the current force acting on the motor vehicle part is determined. This enables acquisition both of very fast and also very slow pinching processes.
Two embodiments of the invention are explained in detail below using the attached drawings.